Acoustic detection of krill from an undersea glider

The GENTOO project aims to investigate the potential for undersea gliders to make high resolution temporal and spatial biological and physical observations of ocean currents and krill distribution to the east of the Antarctic Peninsula. In January 2012 three iRobot Seagliders were deployed to measure temperature, salinity, dissolved oxygen, chlorophyll fluorescence, acoustic backscatter and depth-averaged currents in the upper 1000 m along sections across the Antarctic continental shelf and slope into the Weddell Sea. At the same time a newly developed stand alone echosounder, Imagenex ES853 120 kHz, was integrated into a Seaglider to collect mean volume backscatter measurements of Antarctic krill. We outline the constraints of the glider as an active acoustic platform; present the first results of calibrating the echosounder using a tungsten carbide sphere, discuss validation of target identification by mounting the echosounder onto a Rectangular Midwater Trawl (RMT8) and show data from two short deployments of the echosounder integrated into the glider.